The proliferative response of B lymphocytes to stimulation with anti-IgM antibodies and B cell growth factors was studied in 27 patients with SLE and 17 normal donors. In addition, the expression of messenger RNA of the proto-oncogene c-myc was also studied in B cells from SLE patients and normal donors. The proliferative response of lupus B cells to anti-IgM and B cell growth factors as compared to normal B cells, demonstrated a wide range of response. Ten were lower than normal and 8 were either normal or supernormal. As compared to normals, expression of B cell c-myc RNA from SLE patients was either normal or depressed. In general, in patients with SLE there was a positive correlation between levels of c-myc expression and degree of proliferation in B cells after stimulation with anti-IgM and B cell growth factors.